Flip-chip SMT LEDs with variable number of emitting surfaces

ABSTRACT

A method to make light-emitting diode (LED) units include arranging LEDs in a pattern, forming an optically transparent spacer layer over the LEDs, forming an optically reflective layer over the LEDs, and singulating the LEDs into LED units. The method may further include, after forming the optically transparent spacer layer and before singulating the LEDs, forming a secondary light-emitting layer that conforms to the LEDs, cutting the LEDs to form LED groups having a same arrangement, spacing the LED groups on a support, and forming the optically reflective layer in spaces between the LED groups.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 62/238,666, filed Oct. 7, 2015. U.S. Provisional PatentApplication No. 62/238,666 is incorporated herein.

FIELD OF THE INVENTION

The present disclosure relates to semiconductor light-emitting diodes(LEDs), and more particular to side-emitting surface-mount technology(SMT) LEDs.

BACKGROUND

In illumination and display applications, it is desirable to uniformlyilluminate a diffuser screen using the minimal number of LEDs. In theseapplications, side emission with reduced or suppressed top emission ispreferred. However many LEDs are Lambertian emitters that emit light inan omnidirectional pattern. Thus what is needed is an LED packagingtechnique that transforms Lambertian emitters into LEDs with variablenumber of emitting surfaces (hereafter “N-sided emitters”) with enhancedlateral radiation pattern into specific azimuthal directions.

SUMMARY

In one or more examples of the present disclosure, a method to makelight-emitting diode (LED) units includes arranging LEDs in a pattern,forming an optically transparent spacer layer over the LEDs, forming anoptically reflective layer over the LEDs, and singulating the LEDs intoLED units. The method may further include, after forming the opticallytransparent spacer layer and before singulating the LEDs, forming asecondary light-emitting layer that conforms to the LEDs, cutting theLEDs to form LED groups having a same arrangement, spacing the LEDgroups on a support, and forming the optically reflective layer inspaces between the LED groups.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 illustrates a top view of a packaging process for makingfour-sided emitter packages in examples of the present disclosure;

FIGS. 2 and 3 respectively illustrate a side cross-sectional view and atop view of a four-sided emitter package of FIG. 1 in examples of thepresent disclosure;

FIGS. 4 and 5 illustrate a top view of a packaging process for makingthree-sided emitter packages in examples of the present disclosure;

FIGS. 6 and 7 respectively illustrate a side cross-sectional view and atop view of a three-sided emitter package of FIG. 5 in examples of thepresent disclosure;

FIGS. 8 and 9 illustrate a top view of a packaging process for makingtwo-sided emitter packages in examples of the present disclosure;

FIGS. 10 and 11 respectively illustrate a side cross-sectional view anda top view of a two-sided emitter package of FIG. 9 in examples of thepresent disclosure;

FIGS. 12 and 13 illustrate a top view of a packaging process for makingtwo-sided emitter packages in examples of the present disclosure;

FIGS. 14 and 15 respectively illustrate a side cross-sectional view anda top view of a two-sided emitter package of FIG. 13 in examples of thepresent disclosure;

FIG. 16 illustrates a top view of a packaging process for makingsingle-sided emitter packages in examples of the present disclosure;

FIGS. 17 and 18 respectively illustrate a side cross-sectional view anda top view of a single-sided emitter package of FIG. 16 in examples ofthe present disclosure;

FIG. 19 illustrates a side cross-sectional view of a structure formed byan assembly process for integrating four or five-sided emitters on aprinted circuit board in examples of the present disclosure; and

FIG. 20 is a flowchart of a method to make N-sided emitters in examplesof the present disclosure.

Use of the same reference numbers in different figures indicates similaror identical elements.

DETAILED DESCRIPTION

FIG. 1 illustrates a top view of a level-1 packaging process 100 formaking light-emitting diode (LED) units or packages 101 (only one islabeled in view 120) in examples of the present disclosure. LED units101 may be four-sided emitters that emit from four lateral surfaces. Asshown in a view 102, LEDs 104 (only one is labeled) are placed on asupport 106. LEDs 104 are surface-mount devices that can be mounted orplaced directly onto the surface of interposers or printed circuitboards (PCBs). Each LED 104 has a bottom contact surface and top andside-emitting surfaces. The bottom contact surface includes anode andcathode contacts 108 (shown in phantom). LED 104 may have an area of 0.1millimeter (mm) by 0.1 mm to 10 by 10 mm2 and have a thickness from 10microns (μm) to 1 mm. LEDs 104 may be a flip-chip chip-scale package(CSP) LEDs. A pick-and-place machine picks up LEDs 104 from a tray or areel and places them with their bottom contact surfaces facing down onsupport 106. LEDs 104 are arranged in a pattern on support 106, such asin a square or rectangular matrix 109 where neighboring LEDs 104 arespaced equally apart. Support 106 may be a tacky tape on a metal frame.

As shown in view 110, one or more layers 112, 114, and 116 are formedover LEDs 104 on support 106. Note that the use of the term “over”includes one element being directly atop another element.

In some examples of the present disclosure, a secondary light-emittinglayer 112 is formed over LEDs 104 on support 106. Secondarylight-emitting layer 112, also referred to as a wavelength convertinglayer, converts part of the primary light emitted by LEDs 104 to asecondary light of a different wavelength. The secondary light combineswith the remainder of the primary light to produce a desired color.Secondary light-emitting layer 112 may be a laminate including a layerof titanium oxide (TiOx) (or another translucent or diffusive metaloxide) in silicone followed by a layer of phosphor in silicone. Thelayer of TiOx in silicone has a thickness of 10300 μm, and the phosphorin silicone layer has a thickness of 10-300 μm. A laminating machine maylaminate secondary light-emitting layer 112 over and in-between LEDs 104on support 106. As secondary light-emitting layer 112 is relativelythin, it conforms to the topography of LEDs 104 on support 106. In someexamples secondary light-emitting layer 112 is omitted when only theprimary light is desired.

An optically transparent spacer layer 114 is formed over secondarylight-emitting layer 112. In other examples that are without secondarylight-emitting light 112, transparent spacer layer 114 is formed overLEDs 104 on support 106. Transparent spacer layer 114 encapsulates LEDs104 and provides the proper spacing between LEDs 104 and a subsequentlayer. Transparent spacer layer 114 may be silicone or glass.Transparent spacer layer 114 may have a thickness of 0 to 10 mm (e.g.,675 μm). A molding machine molds transparent spacer layer 114 oversecondary light-emitting layer 112 or LEDs 104 and support 106.Transparent spacer layer 114 has a completely planar top surface or aplanar top surface with indentations, such as inverted cones or dimples,over LEDs 104.

An optically reflective layer 116 is formed over transparent spacerlayer 110. Reflective layer 116 prevents light from exiting through thetop of LED units 101. Reflective layer 116 may be TiOx (or anothertranslucent or diffusive metal oxide) in silicone. Reflective layer 116may have a thickness of 10 to 300 μm. A molding machine may mold areflective layer 116 over transparent spacer layer 110. Reflective layer116 may be molded with a planar top surface. When transparent spacerlayer 114 has inverted cones or dimples on its top surface, reflectivelayer 116 would fill in those indentations. At this point LEDs 104 areheld together by one or more layers 112, 114, and 116.

As shown in view 118, LEDs 104 (only one is labeled) are flipped over bytransferring them to a new support 119 so contacts 108 (only two arelabeled) on their bottom contact surfaces are visible. As shown in view120, the LEDs 104 (only one is labeled) are singulated along orthogonalscribe lanes 122 (only two are labeled) to form individual LED units 101(only one is labeled).

FIGS. 2 and 3 respectively illustrate a side cross-sectional view and atop view of LED unit 101 in examples of the present disclosure. LED unit101 includes LED 104, a secondary light emitter 112-1 over top andside-emitting surfaces of the LED, a transparent spacer 114-1 over thesecondary light emitter, and a reflector 116-1 over a top surface of thetransparent spacer. LED 104 typically has the shape of a rectangularprism but may be another shape such as a cube or a cylinder. Secondarylight emitter 112-1 has the shape of a top hat with a crown thatreceives LED 104 and a brim that surrounds the base of the LED.Transparent spacer 114-1 has the shape of a cap with an opening thatreceives the crown of secondary light emitter 112-1 and a rim that sitson the brim of the secondary light emitter. Reflector 116-1 has theshape of a plate that sits over the top of transparent spacer 114-1. Asshown in FIG. 3, LED unit 101 only emits light from its four lateralsurfaces that are not covered by reflector 116-1.

FIGS. 4 and 5 illustrate a top view of a level-1 packaging process 400for making LED units or packages 401 (only one is labeled in view 424 ofFIG. 5) in examples of the present disclosure. LED units 401 may bethree-sided emitters. Referring to FIG. 4, view 402, LEDs 104 (only oneis labeled) are placed with their bottom contact surfaces facing down onsupport 106. LEDs 104 are placed in a pattern, such as in double rows404 (only one is labeled) of the LEDs. Each double row 404 includes afirst row of LEDs with their contact pads 108 in a first orientation,and a second row of LEDs with the contact pads 108 in a secondorientation that is rotated 180 degrees from the first orientation.

As shown in view 406, secondary light-emitting layer 112 is formed overLEDs 104 on support 106, and optically transparent spacer layer 114 isformed over the secondary light-emitting layer. As secondarylight-emitting layer 112 is relatively thin, it conforms to thetopography of LEDs 104 on support 106. In some examples where only theprimary light is desired, secondary light-emitting layer 112 is omittedand transparent spacer layer 114 is formed over LEDs 104 on support 106.Transparent spacer layer 114 has a completely planar top surface or asubstantially planar top surface with indentations, such as invertedcones or dimples, over LEDs 104. At this point LEDs 104 are heldtogether by secondary light-emitting layer 112 and transparent spacerlayer 114 or the transparent spacer layer alone.

As shown in view 408, LEDs 104 (only one is labeled) are flipped over bytransferring them to a new support 410 so contacts 108 (only two arelabeled) on the bottom contact surfaces of the LEDs are visible. Support410 may be a tacky tape supported by a metal rim. As shown in view 412,LEDs 104 are cut into LED groups 414 having the same arrangement alonghorizontal scribe lanes 416. Each LED groups 414 includes a double row404 of LEDs 104.

Referring to FIG. 5, view 418, LED groups 414 are spaced apart and thenflipped over by transferring them to a new support 420. Support 420 maybe a tacky tape on a metal frame.

As shown in view 422, optically reflective layer 116 is formed over andin-between LED groups 414 (not labeled). Reflective layer 116 preventslight from exiting through the top of LED units 401. Reflective layer116 may be molded with a planar top surface. When transparent spacerlayer 114 of LED groups 412 has inverted cones or dimples on its topsurface, reflective layer 116 would fill in those indentations. At thispoint LED groups 414 are held together by reflective layer 116.

As shown in view 424, LED groups 414 are flipped over by transferringthem to a new support 119 so contacts 108 on the bottom contact surfacesof LEDs 104 are visible. LEDs 104 (only one is labeled) are singulatedinto individual LED units 401 (only one is labeled) along orthogonalscribe lanes 428 (only two are labeled). Vertical scribe lanes 428 atthe ends cut along or slightly into the left and right edges of LEDgroups 414 (only one is labeled) so no reflective layer 116 remain onthose edges. Vertical scribe lanes 428 between the ends cut betweenneighboring LEDs 104. Horizontal scribe lanes 428 cut through reflectivelayer 116 above and below LED groups 414 so portions of the reflectivelayer 116 remains on the top edge of the first row and the bottom edgeof the second row in each LED group.

FIGS. 6 and 7 respectively illustrate a side cross-sectional view and atop view of LED unit 401 in examples of the present disclosure. LED unit401 includes LED 104, secondary light emitter 112-1, transparent spacer114-1, and a reflector 116-2. Reflector 116-2 forms two plates that sitover the top of transparent spacer 114-1 and one side of the transparentspacer and the brim of secondary light emitter 112-1. As shown in FIG.7, LED unit 401 emits light only from three side-emitting surfaces thatare not covered by reflector 116-2.

FIGS. 8 and 9 illustrate a top view of a level-1 packaging process 800for making LED units or packages 801 (only one is labeled in view 820 ofFIG. 9) in examples of the present disclosure. LED units 801 may betwo-sided emitters. Referring to FIG. 8, view 802, LEDs 104 (only one islabeled) are placed with their bottom contact surfaces facing down onsupport 106. LEDs 104 are placed in a pattern, such as in two-by-twoarrays 804 (only one is labeled). Each two-by-two array 804 includes, ina spiral order, a first LED with its contact pads 108 in a firstorientation, a second LED with its contact pads 108 in a secondorientation that is rotated 90 degrees from the first orientation, athird LED with its contact pads 108 in a third orientation that isrotated 90 degrees from the second orientation, and a fourth LED withits contact pads 108 in a fourth orientation that is rotated 90 degreesfrom the third orientation.

As shown in view 806, secondary light-emitting layer 112 is formed overLEDs 104 on support 106, and optically transparent spacer layer 114 isformed over the light-emitting layer. As secondary light-emitting layer112 is relatively thin, it conforms to the topography of LEDs 104 onsupport 106. In some examples where only the primary light is desired,secondary light-emitting layer 112 is omitted and transparent spacerlayer 114 is formed over LEDs 104 on support 106. Transparent spacerlayer 114 has a completely planar top surface or a substantially planartop surface with indentations, such as inverted cones or dimples, overLEDs 104. At this point LEDs 104 are held together by secondarylight-emitting layer 112 and transparent spacer layer 114 or thetransparent spacer layer alone.

As shown in view 808, LEDs 104 (only one is labeled) are flipped over bytransferring them to a new support 410 so contacts 108 (only two arelabeled) on the bottom contact surfaces of LEDs 104 are visible. Asshown in view 810, LEDs 104 (only one is labeled) are cut into LEDgroups 812 (only one is labeled) having the same arrangement alongorthogonal scribe lanes 814 (only two are labeled). Each LED groups 810includes a two-by-two array 804 of LEDs 104.

Referring to FIG. 9, view 816, LED groups 812 are spaced apart and thenflipped over by transferring them to a new support 420.

As shown in view 818, optically reflective layer 116 is formed over andin-between LED groups 812 (not labeled). Reflective layer 116 preventslight from exiting through the top of LED units 801. Reflective layer116 may be molded with a planar top surface. When transparent spacerlayer 114 of LED groups 812 has inverted cones or dimples on its topsurface, reflective layer 116 would be fill in those indentations. Atthis point LED groups 812 are held together by reflective layer 116.

As shown in view 820, LED groups 812 are flipped over by transferringthem to a new support 119 so contacts 108 (only two are labeled) on thebottom contact surfaces of LEDs 104 (only one is labeled) are visible.LEDs 104 are singulated into individual LED units 801 (only one islabeled) along orthogonal scribe lanes 824 (only two are labeled). Afirst set of vertical and horizontal scribe lanes 824 cut throughreflective layer 116 along the edges of each LED group 812 (only one islabeled) so portions of the reflective layer 116 remain on two adjacentlateral surfaces of each LED 104. A second set of vertical andhorizontal scribe lanes 824 cut between neighboring LEDs 104 in each LEDgroup 812 so two adjacent lateral surfaces of each LED 104 are withoutreflective layer 116.

FIGS. 10 and 11 respectively illustrate a side cross-sectional view anda top view of LED unit 801 in examples of the present disclosure. LEDunit 801 includes LED 104, secondary light emitter 112-1, transparentspacer 114-1, and a reflector 116-3. Reflector 116-3 forms three platesthat sit over the top of transparent spacer 114-1 and two adjacent sidesof the transparent spacer and the brim of secondary light emitter 112-1.As shown in FIG. 11, LED unit 801 emits light only from two adjacentside-emitting surfaces that are not covered by reflector 116-3.

FIGS. 12 and 13 illustrate a top view of a level-1 packaging process1200 for making LED units or packages 1201 (only one is labeled) inexamples of the present disclosure. LED units 1201 may be two-sidedemitters. Referring to FIG. 12, view 1202, LEDs 104 (only one is labeledin view 1220 of FIG. 13) are placed with their bottom contact surfacesfacing down on support 106. LEDs 104 are placed in a pattern, such as insingle rows 1204 (only one is labeled) of LEDs 104 having their contactpads 108 (only two are labeled) in the same orientation.

As shown in view 1206, secondary light-emitting layer 112 is formed overLEDs 104 on support 106, and optically transparent spacer layer 114 isformed over the secondary light-emitting layer. As secondarylight-emitting layer 112 is relatively thin, it conforms to thetopography of LEDs 104 on support 106. In some examples where only theprimary light is desired, secondary light-emitting layer 112 is omittedand transparent spacer layer 114 is formed over LEDs 104 on support 106.Transparent spacer layer 114 has a completely planar top surface or asubstantial planar top surface with indentations, such as inverted conesor dimples, over LEDs 104. At this point LEDs 104 are held together bysecondary light-emitting layer 112 and transparent spacer layer 114 orthe transparent spacer layer alone.

As shown in view 1208, LEDs 104 (only one is labeled) are flipped overby transferring them to a new support 410 so contacts 108 (only two arelabeled) on the bottom contact surfaces of LEDs 104 are visible. Asshown in view 1210, LEDs 104 (only one is labeled) are cut alonghorizontal scribe lanes 1214 (only one is labeled) to form LED groups1212 (only one is labeled) having the same arrangement. Each LED groups1212 includes a row 1204 of LEDs 104.

Referring to FIG. 13, view 1216, LED groups 1212 are spaced apart andthen flipped over by transferring them to a new support 420.

As shown in view 1218, optically reflective layer 116 is formed over andin-between LED groups 1212 (not labeled). Reflective layer 116 preventslight from exiting through the top of LED units 1201. Reflective layer116 may be molded with a planar top surface. When transparent spacerlayer 114 of LED groups 1212 has inverted cones or dimples on its topsurface, reflective layer 116 would fill in those indentations. At thispoint LED groups 1212 are held together by reflective layer 116.

As shown in view 1220, LED groups 1212 are flipped over by transferringthem to a new support 119 so contacts 108 (only two are labeled) on thebottom contact surfaces of LEDs 104 are visible. LEDs 104 (only one islabeled) are singulated into individual LED units 1201 (only one islabeled) along orthogonal scribe lanes 1224 (only two are labeled).Horizontal scribe lanes 1224 cut through reflective layer 116 along topand bottom edges of LED groups 1212 (only one is labeled) so portions ofthe reflective layer 116 remain on two opposing lateral surfaces of eachLED unit 1201. Vertical scribe lanes 1224 cut along or slightly intoleft and right edges of LED groups 1212 and between neighboring LEDs 104in each LED group so the other two opposing lateral surfaces of each LEDunit 1201 are without reflective layer 116.

FIGS. 14 and 15 respectively illustrate a side cross-sectional view anda top view of an LED unit 1201 in examples of the present disclosure.LED unit 1201 includes LED 104, secondary light emitter 112-1,transparent spacer 114-1, and a reflector 116-4. Reflector 116-4 formsthree plates that sit over the top of transparent spacer 114-1 and twoopposing sides of the transparent spacer and the brim of secondary lightemitter 112-1. As shown in FIG. 15, LED unit 1201 emits light only fromtwo opposing side-emitting surfaces that are not covered by reflector116-4.

FIG. 16 illustrates a top view of a level-1 packaging process 1600 formaking LED units or package 1601 (only one is labeled) in examples ofthe present disclosure. LED units 1601 may be single-sided emitters.Process 1600 starts with the same steps as process 400 up to view 408(FIG. 4). View 408 may then be followed by view 1602 where LEDs 104(only one is labeled) are cut along orthogonal scribe lanes 1604 (onlytwo are labeled) to form LED groups 1606 (only one is labeled) havingthe same arrangement. Each LED groups 1606 includes two verticallyadjacent LEDs 104 in the same double row 404 (FIG. 4) and the twovertically adjacent LEDs have their contact pads in orientations thatare 180 degrees apart.

As shown in view 1608, LED groups 1606 (only one is labeled) are spacedapart and flipped over by transferring them to a new support 420.

As shown in view 1610, optically reflective layer 116 is formed over andin-between LED groups 1606 (not labeled). Reflective layer 116 preventslight from exiting through the top of LED units 1601. Reflective layer116 may be molded with a planar top surface. When transparent spacerlayer 114 of LED groups 1606 has inverted cones or dimples on its topsurface, reflective layer 116 would fill in those indentations. At thispoint LED groups 1606 are held together by reflective layer 116.

As shown in view 1612, LED groups 1606 (only one is labeled) are flippedover by transferring them to a new support 119 so contacts 108 (only twoare labeled) on the bottom contact surfaces of LEDs 104 are visible.LEDs 104 (only one is labeled) are singulated into individual LED units1601 (only one is labeled) along orthogonal scribe lanes 1616 (only twoare labeled). Vertical scribe lanes 1616 and a first set of horizontalscribe lanes 1616 cut through reflective layer 116 along the perimeterof each LED group 1606 so portions of the reflective layer 116 remain onthree adjacent lateral surfaces of each LED unit 1601. A second set ofhorizontal scribe lanes 1616 cut between LEDs 104 in each LED group 1606so one lateral surface of each LED unit 1601 is without reflective layer116.

FIGS. 17 and 18 respectively illustrate a side cross-sectional view anda top view of an LED unit 1601 in examples of the present disclosure.LED unit 1601 includes LED 104, secondary light emitter 112-1,transparent spacer 114-1, and a reflector 116-5. Reflector 116-5 formsfour plates that sit over the top of the transparent spacer 114-1 andthree adjacent sides of the transparent spacer and the brim of secondarylight emitter 112-1. As shown in FIG. 18, LED unit 1601 emits light onlyfrom one side-emitting surface that is not covered by reflector 116-5.

FIG. 19 illustrates a side cross-sectional view of a structure or lightengine 1900 formed by a level-2 assembly process for integrating LEDunits 1901 on a PCB 1902 in examples of the present disclosure. LEDunits 1901 may be five-sided emitters that emit light from its top andside-emitting surfaces. Alternatively LED units 1901 may be four-sidedemitters that have reflectors 1903 on their top so they emit light fromtheir sides. For example LED units 1901 may be LED units 101 (FIGS. 1 to3). PCB 1902 includes traces that connect LED units 1901 in series orparallel. A number of methods may be used to fix LED units 1901 to PCB1902. For example solder paste is applied to bonding areas on PCB 1902and LED units 1901 are picked and placed on the bonding areas, and thePCB with the LED units are sent through a reflow oven to fix the LEDunits to the PCB.

To enhance lateral radiation patter into specific azimuthal directions,a reflective material is dispensed between LED units 1901 or on selectedsides of the LED units. The reflective material may be TiOx (or anothertranslucent or diffusive metal oxide) in silicone. As a result ofcapillary action, the reflective material forms reflective fillets 1904that cover the selected sides of LED units 1901 to create the desiredradiation pattern. For example, reflective fillets 1904 may coveradjacent sides, opposing sides, three sides of each LED unit 1901.

FIG. 20 is a flowchart of a method 2000 to make N-sided emittersdescribed above in examples of the present disclosure. Method 2000 maybegin with block 2002.

In block 2002, LEDs 104 are arranged in a pattern. As described above,the pattern may be a square or rectangular matrix 109 (FIG. 1), doublerows 404 (FIG. 4), two-by-two arrays 804 (FIG. 8), or single rows 1204(FIG. 12). Block 2002 may be followed by optional block 2004.

In optional block 2004, secondary light-emitting layer 112 is formedover and conforms to LEDs 104. Optional block 2004 may be skipped whenonly the primary light is desired. Optional block 2004 may be followedby block 2006.

In block 2006, optically transparent spacer layer 114 is formed oversecondary light-emitting layer 112 or LEDs 104 when the secondarylight-emitting layer is omitted. Block 2006 may be followed by optionalblock 2008.

In optional block 2008, LEDs 104 are flipped and cut into LED groups. Asdescribed above, the LED groups may be LED groups 414 (FIG. 4), 812(FIG. 8), 1212 (FIG. 12), or 1606 (FIG. 16). Optional block 2008 may beskipped when making four-sided emitters 101. Optional block 2008 may befollowed by optional block 2010.

In optional block 2010, the LED groups are spaced apart and flipped overor vice versa. Optional block 2010 may be skipped when making four-sidedemitters 101. Optional block 2010 may be followed by block 2012.

In block 2012, optically reflective layer 116 is formed over LEDs 104when making four-sided emitters or over the LED groups when makingthree, two, or single-sided emitters. Block 2012 may be followed byoptional block 2014.

In optional block 2014, reflective layer 116 is formed in spaces betweenthe LED groups when making three, two, or single-sided emitters. Block2012 and optional block 2014 may be the same step as reflective layer116 is molded over and in-between the LED groups. Optional block 2014may be followed by block 2016.

In block 2016, LEDs 104 or the LED groups are flipped and singulatedinto LED units. The LED units may be LED units 101 (FIG. 1), 401 (FIG.4), 801 (FIG. 8), 1201 (FIG. 12), or 1601 (FIG. 16). The LED units maybe tested, binned, and stored in a reeled tape. Blocks 2002 to 2016 maybe part of a level-1 packaging process. Block 2016 may be followed byoptional block 2018.

In block 2018, the LED units are surface mounted on a PCB to form astructure such as a light engine. Optional block 2018 may be followed byoptional block 2020.

In block 2020, a reflective material is dispensed between or on thesides of the LED units on the PCB. The reflective material forms filletsthat cover selected sides of the LED units so the resulting structuregenerates a desired radiation pattern. For example, reflective materialis dispensed between and on the sides of LED units 1901 (FIG. 19) on PCB1902 (FIG. 19) to create fillets 1902 (FIG. 19) on selected sides of theLED units.

Various other adaptations and combinations of features of theembodiments disclosed are within the scope of the invention. Numerousembodiments are encompassed by the following claims.

The invention claimed is:
 1. A method of forming side emittinglight-emitting diode (LED) units, the method comprising: arranging aplurality of LEDs in a pattern on a temporary support; forming asecondary light-emitting layer that conforms to the plurality of LEDs,covering top and side-emitting surfaces of each of the plurality ofLEDs: after forming the secondary light-emitting layer, forming anoptically transparent spacer layer over the plurality of LEDs; formingan optically reflective layer over the optically transparent spacerlayer to form a structure that includes at least the plurality of LEDs,the secondary light-emitting layer, the optically transparent spacerlayer and the optically reflective layer; and after the opticallyreflective layer is formed over the optically transparent spacer layer,singulating the structure into a plurality of LED units, each of theplurality of LED units including at least one of the plurality of LEDs,a portion of the secondary light-emitting layer, a portion of thetransparent spacer layer formed over the at least one of the pluralityof LEDs, and a portion of the reflective layer formed over the portionof the transparent spacer layer.
 2. The method of claim 1, furthercomprising, after forming the optically reflective layer and beforesingulating the structure into the plurality of LED units, flipping thestructure.
 3. The method of claim 1, wherein the singulating thestructure into the plurality of LED units further comprises singulatingthe structure to form a plurality of four-sided emitters, each of theplurality of four-sided emitters comprising: one of the plurality ofLEDs, the portion of the optically transparent spacer formed over theone of the plurality of LEDs, and the portion of the opticallyreflective layer formed over the portion of the optically transparentspacer.
 4. The method of claim 1, wherein the singulating the structureinto the plurality of LED units further comprises singulating thestructure to form a plurality of four-sided emitters, each of theplurality of four-sided emitters comprising: one of the plurality ofLEDs, the portion of the secondary light emitting layer formed over thetop and side-emitting surfaces of the one of the plurality of LEDs, theportion of the optically transparent spacer layer formed over theportion of the secondary light emitting layer, and the portion of theoptically reflective layer formed over the portion of the opticallytransparent spacer.
 5. The method of claim 1, wherein the secondarylight-emitting layer comprises a laminate including a first layer ofphosphor in silicone and a second layer of titanium oxide in silicone.6. The method of claim 1, wherein forming the optically transparentspacer layer comprises molding dimples in the optically transparentspacer layer over the plurality of LEDs.
 7. The method of claim 1,wherein the optically transparent spacer layer comprises silicone andthe optically reflective layer comprises titanium oxide in silicone. 8.A method of forming side emitting light-emitting diode (LED) units, themethod comprising: arranging a plurality of LEDs in a pattern on atemporary support; forming an optically transparent spacer layer overthe plurality of LEDs to form a first structure that includes at leastthe plurality of LEDs and the optically transparent spacer layer;cutting the first structure to form a plurality of LED groups; arrangingthe plurality of LED groups on a second temporary support such thatspaces are formed between adjacent LED groups on the second temporarysupport; forming a single optically reflective layer over the opticallytransparent spacer layer of each of the plurality of LED groups on thesecond temporary support such that the single optically reflective layeris also formed in the spaces between the adjacent LED groups to form asecond structure; and after forming the single optically reflectivelayer over the optically transparent spacer layer, singulating thesecond structure to form a plurality of one-side emitting, two-sideemitting or three-side emitting LED units.
 9. The method of claim 8,further comprising, after forming the optically transparent spacer layerand before cutting the first, structure, flipping the first structure.10. The method of claim 8, further comprising, after cutting the firststructure and before arranging the plurality of LED groups, flippingeach of the plurality of LED groups.
 11. The method of claim 10, furthercomprising, after forming the single optically reflective layer andbefore singulating the second structure, flipping the second structure.12. The method of claim 8, further comprising, after arranging theplurality of LEDs on the temporary support and before forming theoptically transparent spacer layer, forming a secondary light-emittinglayer that conforms to the plurality of LEDs, covering top andside-emitting surfaces of each of the plurality of LEDs.
 13. The methodof claim 12, wherein: the arranging the plurality of LEDs in the patterncomprises placing double rows of LEDs on the temporary support, eachdouble row comprising a first row of LEDs having contact pads in a firstorientation and a second row of LEDs having contact pads in a secondorientation that is rotated 180 degrees from the first orientation, theLED groups each comprise a double row of LEDs, and the singulating thesecond structure further comprises singulating the second structure suchthat a portion of the optically reflective layer covers a top surface ofeach of the plurality of LED units and a single lateral surface of eachof the plurality of LED units to form a plurality of three-side emittingLED units.
 14. The method of claim 12, wherein: the arranging theplurality of LEDs in the pattern comprises placing two-by-two arrays ofLEDs on the temporary support, each of the two-by-two arrays comprising,in a spiral order, a first LED having contact pads in a firstorientation, a second LED having contact pads in a second orientationthat is rotated 90 degrees from the first orientation, a third LEDhaving contact pads in a third orientation that is rotated 90 degreesfrom the second orientation, and a fourth LED having contact pads in afourth orientation that is rotated 90 degrees from the thirdorientation, the LED groups each comprise one of the plurality oftwo-by-two arrays, and the singulating further comprises singulating thesecond structure such that a portion of the optically reflective layercovers a top surface of each of the plurality of LED units and twolateral surfaces of each of the plurality of LED units to form aplurality of two-side emitting LED units.
 15. The method of claim 12,wherein: the arranging the plurality of LEDs in the pattern comprisesplacing rows of LEDs of a same orientation on the temporary support, theLED groups each comprise a single row of LEDs, and the singulatingfurther comprises singulating the second structure such that a portionof the optically reflective layer covers a top surface of each of theplurality of LED units and two lateral surfaces of each of the pluralityof LED units to form a plurality of two-side emitting LED units.
 16. Themethod of claim 12, wherein: the arranging the plurality of LEDs in thepattern comprises placing double rows of LEDs on the temporary support,each double row comprising a first row of LEDs having contact pads in afirst orientation and a second row of LEDs having contact pads in asecond orientation that is rotated 180 degrees from the firstorientation, the LED groups each comprise two vertically adjacent LEDsin a double row of LEDs, and the singulating further comprisessingulating the second structure such that a portion of the opticallyreflective layer covers a top surface of each of the plurality of LEDunits and two lateral surfaces of each of the plurality of LED units toform a plurality of two-side emitting LED units.
 17. A method of formingside emitting light-emitting diode (LED) units, the method comprising:arranging a plurality of LEDs in a pattern on a temporary support;forming an optically transparent spacer layer over all of the pluralityof LEDs on the transparent substrate; forming an optically reflectivelayer over the optically transparent spacer layer, covering an entiresurface of the optically transparent spacer layer or an interveninglayer, to form a structure that includes at least the plurality of LEDs,the optically transparent spacer layer and the optically reflectivelayer; after forming the optically reflective layer and beforesingulating the structure into the plurality of LED units, flipping thestructure; and after the optically reflective layer is formed over theoptically transparent spacer layer, singulating the structure into aplurality of LED units, each including at least one of the plurality ofLEDs, a portion of the transparent spacer surrounding top and sidesurfaces of the at least one of the plurality of LEDs, and a portion ofthe reflective layer formed over the portion of the transparent spacerlayer.
 18. The method of claim 17, wherein the singulating the structureinto the plurality of LED units further comprises singulating thestructure to form a plurality of four-sided emitters, each of theplurality of four-sided emitters comprising: one of the plurality ofLEDs, the portion of the optically transparent spacer formed over theone of the plurality of LEDs, and the portion of the opticallyreflective layer formed over the portion of the optically transparentspacer.
 19. The method of 17, wherein: the singulating the structureinto the plurality of LED units further comprises singulating thestructure to form a plurality of four-sided emitters, each of theplurality of four-sided emitters comprising: one of the plurality ofLEDs, a portion of a secondary light emitting layer formed over the topand side-emitting surfaces of the one of the plurality of LEDs, theportion of the optically transparent spacer layer formed over theportion of the secondary light emitting layer, and the portion of theoptically reflective layer formed over the portion of the opticallytransparent spacer.